The invention particularly refers to autoinjectors which are medical devices designed to deliver a single dose of a particular medicament. Autoinjectors are easy to use and are intended for self-administration by patients, or for administration by untrained personnel. However, the present invention is not limited to this type of injection devices but is also applicable to syringes and pens which enable accurate and controlled dosage prior injection and which are reusable or disposable.
Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc.
Today's known autoinjectors keep the needle tip shielded prior to injection and also comprise a passive safety mechanism to prevent accidental firing (injection). Just by pressing a release button, the syringe needle is automatically driven out and the medicament is delivered.
One of the problems using such autoinjectors is that the often the full dose is not delivered because of several reasons. However, it is necessary to administer the full dose in order to reach full effectiveness of the medicament within the treated body of human being or animal. Hence, for easier recognition of full delivery, some autoinjectors available at the market have a visual indication to confirm that the full dose was spent.
Document EP 0 730 876 B1 discloses a medical dispensing device comprising an end-of-dose click arrangement which creates an audible “click” sound thereby providing an audible confirmation that the entire dosage has been injected. This sound is produced by an edge of a flexible finger moving past a housing edge and into a groove.
Further, from document WO 2006/079481 A1 an injection device with a dose delivering mechanism and an end of dose feedback mechanism is known. Therein a first and a second part of an injection device are adapted to perform a relative rotational movement with respect to each other during injection of a dose. The relative rotational movement causes at least two parts of the injection device to abut or engage, the abutment or engagement causing a non-visual feedback signal to be generated. This may be generated, e.g., by a change in rotational velocity of at least one part of the injection device, for example by changing a pitch of a threaded portion, or by engaging a non-rotating part and a rotating part thereby causing the non-rotating part to start rotating.
The disadvantage of the above state of the art end-of-dose indications is that they may be overheard or can only hardly be recognized in a tactile manner. A single click sound in a loud environment is easily overheard. A change of velocity of a rotational movement may be not as clear and distinct enough that a user clearly feels a tactile signal.